Micro-Electro-Mechanical Systems (MEMS) inertial measurement units contain three gyroscopes and three accelerometers for detecting changes in attitude and acceleration. Typically, the three gyroscopes and the three accelerometers are mounted on separate orthogonal axis, each with their own set of control and read-out electronics. It is appreciated that there is an inherent cost in the assembly of the MEMS inertial measurement unit in view that the three gyroscopes and the three accelerometers must be precisely installed, in view that a relatively large amount of processing capacity is required to process information form six separate units, and in view of the power source requirements to power the three gyroscopes and the three accelerometers. Many applications require a reduction in size, computational requirements, power requirements, and cost of a MEMS inertial measurement unit. In view of these constraints, it would be advantageous to reduce the number of sensing devices in a MEMS inertial measurement unit.
A conventional MEMS gyroscope may be used to determine angular rotation by measuring Coriolis forces exerted on resonating proof masses. A conventional MEMS gyroscope includes two silicon proof masses mechanically coupled to and suspended from a substrate, typically glass, using one or more silicon flexures. A number of recesses etched into the substrate allow selective portions of the silicon structure to move back and forth freely within an interior portion of the device. In certain designs, substrates can be provided above and below the silicon structure to sandwich the proof masses between the two substrates. A pattern of metal traces formed on the substrate(s) can be used to deliver various electrical bias voltages and signal outputs to the device.
A drive system for many MEMS gyroscopes typically includes a number of drive elements that cause the proof mass to oscillate back and forth along a drive axis perpendicular to the direction in which Coriolis forces are sensed. In certain designs, for example, the drive elements may include a number of interdigitated vertical comb fingers configured to convert electrical energy into mechanical energy using electrostatic actuation. Such drive elements are described, for example, in U.S. Pat. No. 5,025,346 to Tang et al., entitled “LATERALLY DRIVEN RESONANT MICROSTRUCTURES,” and U.S. Pat. No. 7,036,373 to Johnson et al., entitled “MEMS GYROSCOPE WITH HORIZONTALLY ORIENTED DRIVE ELECTRODES,” both of which are incorporated herein by reference in their entirety.
Other types of MEMS devices may be used to measure both linear acceleration and rotation. However, such MEMS devices are operated in an open loop mode wherein the acceleration and rotation (gyro) responses are coupled with and depend on each other. Accordingly, systems that independently measure both linear acceleration and rotational movement require at least two different devices so that the acceleration sensing is decoupled from the rotation sensing, which may result in increased complexity and costs.